High power impulse magnetron sputtering (HiPIMS) prepared ultrathin gold film for plasmonic biosensor application

The global pandemic of coronavirus disease 2019 (COVID-19) has come to a different stage worldwide. Until now, the common flu-like outbreaks have led to increasing demand for screening tests with high sensitivity and specificity. Among biosensors, the noble metal nano-optical sensor based on localized surface plasmon resonance (LSPR) has great potential due to its simple design, feasible manufacturing, and fast response. To develop an efficient and economic examination, this study utilizes high power impulse magnetron sputtering (HiPIMS) to prepare ultrathin gold film (UTGF) on glass substrate. The experimental results show that with an increase in the deposition time from 3 s to 144 s, the UTGF forms from an island-like morphology, a network structure, to ultimately a smooth UTGF layer on glass. When the UTGF sample is conjugated with human serum albumin (HSA) at 5 × 10⁻⁴ M as a pretest analyte, a significant peak shift of 25.6 nm was detected for the UTGF deposited at 12 s. Based on the UV-Vis measurement, the plasmonic loss peak of the UTGF sample with deposition times of 6 s, 12 s, and 24 s are 537.1 nm, 601.9 nm, and 665.8 nm, respectively, whereas the deposition time of 12 s prepared UTGF sample revealed the strongest LSPR effect. With a prolonged deposition time over the percolation time (48 s), those UTGF samples gave no LSPR response. To further detect viral antigen, recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid (N) protein, the UTGF were functionalized with mouse anti-human immunoglobulin G (IgG). The HiPIMS prepared UTGF sample feasible for SARS-CoV-2 detection is demonstrated, giving potential application on rapid and ultrasensitive biomolecules sensor.